You are correct on the aggregate, but that doesn't necessarily work when applied to each individual driver.

I'm a pretty attentive and cautious driver. In the 20 years I have been driving I've been in one accident and that was because another driver was attempting to make an illegal left turn, came across two lanes of traffic, and t-boned me. So if self driving vehicles are only doing better than the worst human drivers, I'm going to be pretty hesitant to turn over control. I'd be in favor of that other driver that hit me using an autonomous vehicle though.